Protecting electrical instruments from excessive electrical surges



July 30, 1935. c. F. NELSON -PRO TECTING ELECTRICAL INSTRUMENTS FROM EXCESSIVE ELECTRICAL SURGES Filed May 16, 1932 ZSnoeritor C 1 N'eZoon Gttorneg Patented July 30, 1935 t UNITED STATES PATENT OFFICE PROTECTING ELECTRICAL INSTRUMENTS FROM EXCESSIVE ELECTRICAL SURGES Crescent F. Nelson, New Dorp, N. Y., assignor to The Western Union Telegraph Company, New York, N. Y., a corporation of New York Application May 16, 1932, Serial No. 611,749

11 Claims. 7 (or. 175-294) This invention relates to the protection of elec- I have shown a Heurtley magnifier HM as an trical instruments which are liable to be injured illustration of an instrument that may be proby excessive surges from lightning or other tected by my invention. The line coil 2 of the sources. e instrument is inserted across the bridge between The object ofthe invention is to provide means the cable terminal and the artificial line AL and 5 for automatically short-circuiting the coil or part is mechanically connected'by the threads 3 with of an instrument connected to a line or cable the suspension of the hot wires 4 of the instruwith such rapidity that the main surge will be ment. safely shunted around the instrument The actuating elements of the protector are W It has been the common practice to disconnect connected through a transformer T to the bridge the line'or cable from the apparatus and connect upon opposite sides of the coil 2. The transformit to ground during the continuance ofa lighter may have a step-up ratio of perhaps I to Hi. ning storm. This precaution is usually taken to The tubes T1, T2, T3 are of the electrostatically protect the delicate receiving apparatus, such as controlled arc discharge yp in which the 1'- r the Heurtley magnifiers which are generally used rent in the plate circuit continues to flow unaf- 15 on long sections of unloaded telegraph cables. fected by the grid voltage after the arc hasbeen Inasmuch as lightning storms may occur at any established by the application of the critical volt time, it is often necessary to delay urgent traffic, age to the grid. For purposes ofillustration I rather than incur the risk of breaking the maghave shown tubes of the gaseous conduction type sertion and relining of a new one and require conting cathode 8 and a grid 9 of inverted cup shape siderable time. i composedof fine wire mesh. Theaction of the Protective devices of the electro-magnetic typetube in continuing the discharge unaffected by do not act with sufiicient rapidity and require an the grid voltage and until the voltage of the plate 00 nifier suspension which would necessite the inhaving a separate heater 'l'for the electron emitappreciable amount of energy to operate. Fur- I0is reduced or stopped, is attributed to the for- 25 thermore it is not feasible to operate an'electromation of a sheath of positive ions around the magnetic device'at the frequencies occurring in grid, usually only a fraction of a millimeter in lightning surges. In order to overcome the diffithickness, which contains the entire voltage drop culties which have heretofore prevented the sucbetween the'grid and the surrounding space. 0 cess of a protective device for such purposes, I Varying the potential of the grid merely changes 0 have provided a device which is voltage controlled the thickness of this sheath without affecting the and which operates unerringly at the frequencies potential of the remaining space. The action of occurring in lightning surges and yet is unrethe grid may, therefore, be likened to a trigger sponsive to normal signaling impulses; To this which is effective to initiate the discharge but end I .employ a protective apparatus which einwhich has no further influence on the discharge, 35 "bodies electrostatically controlled arc discharge being thus distinguished from the usual audion tubes having the characteristic of instantly causgrid, which exerts a continuous influence on the ing the current in a local circuit to flow at, the discharge through the tube. The theory of operfull value of the generator therein upon the apation is set forth in an article by Dr. Albert W. plication of a starting voltage applied to a'grid Hull entitled Hot-Cathode 'I'hyratrons pub- 40 I "member of the tube. The grid element thus acts lished in the General Electric Review Vol. 32, No.

as at1-igger electrode which serves'to instantly 4 April 1929. initiate a discharge across the are included in the The resistance R1 is so adjusted that the negalocal operating circuit. The tubes are so artive bias on the grids of tubes T1 and T2 prevents ranged that the initial surge or either polarity the operation of the tubes during the reception 45 operates the device to apply theprotection. v of normal signals. Resistance R2 isemployed to For'the' pu'rposeof more'adedhately disclosing limit the steady biasing current through the rethe invention I shall refer to the accompanying sistance R1. R3 and R4 are appropriate grid redrawing, which is a circuit diagram illustrating sistors, their value depending upon the particu- 0 in the usualconventional'manner a duplex bridge lar tubes employed. arrangement at a terminal of a telegraphcable The operation of my protector device will be andshowing myprotective deviceadapted to apevident to engineers and those familiar with cirply'ashort circuit about aHe'urtley magnifier incuits of this character. If a surge occurs, due to strument upon the occurrence of an excessive lightning or other cause, impressing a potential electricalsurge. v upon the primary of the transformer T through the condensers c1, c2 which impresses a voltage upon the secondary coil sufiicient to raise the voltage on the grid of one of the tubes to the critical value, it will instantly cause that tube to discharge through its plate circuit, thus starting the flow of current from the plate battery 52 which will thereafter continue to flow until stopped by external means. If the initial potential of the surge is positive, the tube T1 will start and a current will flow from battery I 2 through conductor l4, resistance R7, relay 15, through tube T1, resistance R1 and conductor It to negative pole of the battery. The armature of the relay closes a short circuit through the conductors l1 and it around the line coil 2 of the instrument. This short circuit occurs so quickly (micro-seconds) that the movement of the coil 2, if any, is so slight that noviolent motion can be transmitted to the hot wires 4 or their suspension. In other words, before the inertia of the coil is overcome, it becomes short circuited and consequently any tendency to mo ve is immediately damped. If the initial potential of the surge is in the opposite direction, it is evident that the current would flow through the relay and the tube T2 instead of through the tube T1, the plates of these tubes being connected in parallel to the relay.

As previously stated, the tubes employed have the characteristic of operating at full value the instant the discharge takes place and hence the relay is actuated with great rapidity. Inasmuch as the grid operates with a trigger action to start the tube and thereafter has no control over the operation of the tube, provision must be made for stopping the tube. For this purpose I have shown a third tube T3 with circuit arrangements which cause it to start a predetermined interval after one of the other tubes and its operation immediately extinguishes said other tube. This feature is the invention of H. F. Wilder and is covered in another application Serial No. 615,211 filed June 3, 1932.

When neither of the tubes T1, T2 is operating? their plates ID will assume the full voltage of battery I2 (assume 115 volts). The instant the tube T1 is started, the voltage of its plate will drop from 115 volts to perhaps 15 volts, 3. drop of volts. Inasmuch as theplate of tube T3 is connected to the plate of Tube T1 through the condenser C4, it is subjected to a corresponding drop. The voltage on the grid of ,tube T3 builds up during a predetermined period, depending upon the constants in its grid circuit determined by the condenser 03 and resistance R5. When the potential on the grid reaches its critical value and the tube is started into operation, the voltage on its plate instantly drops from to 15 volts and as the plates of the tubes T3 and T1 are connected through the condenser 0,1, the plate of tube T1 must also instaneously decrease by the same amount, which lowers it to minus 85 volts which momentarily stops the current and the production of ions. If the condenser is large enough so that the ions in the space between the grid and the anode have time to diffuse to the walls of the tube before the anode voltage again becomes positive, the grid, now negative, prevents the current from restarting. In this manner the auxiliary tube Ta stops the flow of current in whichever tube the, current is started and is itself stopped upon the starting of either of said tubes T1 or T2. The current in the auxiliary or stopping tube T3 may be several times smaller than that through the operating tubes T1 and T2, the amount of current being controlled by the limiting resistance B6. The manner in which one tube operates to stop another tube as above described is set forth in the Proceedings of the National Academy of Science, Vol. 15, No. 3, page 218 and also in an article by Dr. Hull entitled Hot-Cathode Thyratrons, published in the General Electric Review Vol. 32 No. 7, July 1929.

It is not necessary, of course, to keep the protective device in service at all times as lightning storms are not liable to occur during certain seasons and weeks or months may elapse without the necessity for using the device. When distiu'bances indicate that excessive surges are liable to occur, the attendant in charge will connect the protective circuits, adjusting the biasing resistance R1, if necessary, so that the tubes T1 and T2 are not affected by the normal signals being received. Business may therefore be transacted over the cable without the interruption which has heretofore occurred upon the approach of a storm. If a surge occurs, one or the other of the tubes T1 or T2 will be started and for the very brief interval during which they are in operation, the siphon of the recording instrument will move to zero position. This informs the receiving operator that a surge has occurred and it will be necessary to have that particular part of the message repeated. In other words, during lightning storms, instead of discontinuing the operation of the cable altogether, it will only be necessary to handle a few extra RQs (service repeat messages).

I have illustrated-one embodment of this invention but it will be obvious to engineers thatvarious modifications can be made to adapt it to different conditions. Instead of employing the tube T3 to extinguish the arc in'the other tubes after a predetermined interval, I may accomplish this purpose by means of a slow acting relay, conne zting the relay winding and its contact in series with the common anode circuit of the tubes T1 and T2. The contact must be arranged to open at the end of the stroke of the armature. Instead of shunting the instrument to be protected it may be preferable under certain conditions to open its circuit during the predetermined protecting interval.

I claim: I

1. In a signaling system including an instrument responsive to signaling impulses, means for protecting the instrument from excessive voltages such as lightning discharges, comprising a shunting device and electrostatically controlled thermionic means non-responsive to signaling impulses but responsive to excessive voltages and operatively connected to actuate said shunting device.

2. In a signaling system including an instrument responsive to signaling impulses, means for protecting the instrument from excessive voltages such as lightning discharges, comprising a shunting device and electrostatically controlled means non-responsive to signaling impulses but responsive to excessive voltages of either polarity operatively connected to actuate said shunting device, and electrostatically controlled means operating to deenergize said shunting device after a predetermined interval.

3. In a signaling system' including an instrument responsive to signaling impulses, means for protecting the instrument from excessive voltages such as lightning discharges, an electrostatically controlled actuating device for said protecting means responsive only to voltages greater than the signaling impulses and electrostatically controlled means for deenergizing said actuating device after a predetermined interval. a 4. In a signaling system including 'an instru ment responsive to signaling impulses, means for protecting the instrument from excessive voltages such as lightning discharges, comprising a relay controlling a shunt around said instrument, a local circuit including a-generator and said relay, and electrostatically controlled trigger means non-responsive to signaling impulses but responsive instantaneously to excessive voltages to close said local circuit.

5. In a signaling system including an instrument responsive to signaling impulses, means for protecting the instrument from excessive voltages such as lightning discharges, comprising a relay controlling a shunt around said instrument, a local circuit including a generator and said relay, and electrostatically controlled trigger means non-responsive to signaling impulses but responsive instantaneously to excessive voltages to start the operation of said local circuit, and electrostatically controlled means associated with said circuit to stop its operation after a predetermined interval.

6. In a signaling system including an instrument responsive to signaling impulses, the combination of electrostatically controlled means for protecting the instrument from excessive voltages such as lightning discharges, of a relay to actuate said protective means, a local circuit including said relay, a current source, and a gaseous conduction device and electrostatically controlled means responsive to an excessive voltage in the system for initiating a discharge through said device.

, dium.

8. In combination; with apparatus for the reception and utilization of electric impulses from a ton line or cable, a protective device for shielding said apparatus from excessive voltage conditions, comprising a local circuit including a current source and an ionizable medium, actuating means for said device in said circuit, electrostatically controlled means responsive to an excessive voltage on said line or cable for initiating a discharge through said ionizable medium, said initiating means being inefiective to further control the discharge, and means for automatically interrupting said discharge after a predetermined interval.

9. In a communication system, receiving apparatus responsive to signaling impulses froma transmission line or cable, a protective device operating to shield said appartus from excessive voltage conditions, a local circuit including a ctu rent source, an actuator for said protective device andan electrostaticallycontrolled gas discharge tube in said local circuit, said tube being responsive to excessive voltage conditions but unaffected by signaling impulses, a starting element or grid in said tube connected to be subjected to voltages on said line or cable, said tube operating irrespective of grid potential after being started,- and electrostatically controlled means associated with said local circuit for stopping the operation ofsaid tube after a predetermined interval.

10. In a signalingsystem including an instru-,

ment responsive to signaling impulses, means for protecting the instrument from excessive voltages such as lightning discharges, comprising a local circuit including a current source and an actuating element for said protecting means, a pair of electrostatically controlled gas discharge tubes connected to said circuit and responsive respectively to positive and negative impulses of excessive voltage but unresponsive to signaling impulses, the grid elements of said tubes being subjected to the voltages of the system, and means operating to automatically stop either tube afte a predetermined interval.

11. In a signaling system as defined in claim 10, said stopping means comprising a third electro; statically controlled gas discharge tube connected to said local circuit and so arranged that it operates a predetermined interval after the starting of either of the other tubes, its operation serving to extinguish the operating tube and being itself stopped upon the starting of either of said tubes.

CRESCENT F. NELSON. 

